Nodular cast iron foundation pile pipe and a method for preparing same

ABSTRACT

The present invention provides a nodular cast iron foundation pile pipe and a method for preparing same, including following steps: (1) preparation before pipe casting: including molten iron preparation, spheroidization and coating spraying on an inner wall of a pipe mold; (2) pipe casting process: including centrifugal casting and pipe drawing; (3) annealing process; (4) finishing process. The present invention further provides the foundation pile pipe manufactured with the above-mentioned method wherein the flange and the foundation pile pipe are integrally cast or welded. In the present invention, the nodular cast iron is used as the material of the foundation pile pipe instead of Q345 steel used in the prior art. As a result, the overall strength is enhanced. The present invention possesses advantages such as corrosion resistance, long service life, low manufacturing cost, low labor intensity, short construction period and being suitable for mechanized construction.

TECHNICAL FIELD

The present invention relates to a foundation pile pipe and a technologyfor preparing same, particularly relates to a nodular cast ironfoundation pile pipe and a technology for preparing same.

BACKGROUND

A pile pipe is a foundation pipe of the pile, which is struckunderground to work as a foundation. A flange thereof is used to connectwith a pole on the ground generally by bolts. The pile pipe is used toreplace the traditional reinforced concrete foundation. To construct thereinforced concrete foundation, it is necessary to dig a big hole,pre-bury reinforcing steel bars and grout cement mortar, and thefoundation can only be used after being cured for a predetermined time.It requires high labor intensity and long construction time. However,the pile pipe foundation is a foundation formed by striking the pilepipe into the ground with a pile driver, and the pole on the ground canbe directly mounted thereto. This technology is suitable for mechanizedconstruction, with low labor intensity and short construction time.

In the prior art, a welding process is used to connect a pipe body ofthe pile pipe with the flange. Q345 steel pipe is used as the materialof the pipe body, and Q345 steel plate is used as the material of theflange. The Q345 meets the requirement of “High strength low alloystructural steels” GB/T1591-94. During the preparation process, firstly,the Q345 steel plate is used to form the flange, on which bolt holes areprocessed according to the needs of design, and then the flange and theQ345 steel pipe is welded together after butt joint, thus a pile pipewith flange is prepared after a preservative treatment.

SUMMARY OF THE INVENTION

In view of the above-mentioned technical problems, the present inventionprovides a nodular cast iron foundation pile pipe and a technology forpreparing same. In the present invention, the nodular cast iron is usedas the material of the foundation pile pipe instead of the Q345 steelpipe used in the prior art, the flange and the foundation pile pipe areintegrally cast or welded, and the foundation pile pipe is produced bycombining with the nodular cast iron pipe process, so as to achieveenhanced overall strength of the production and good corrosionresistance. The nodular cast iron is widely applied to industry, such asthe fields including automobile, metallurgy, and water and gas pipelines. The characteristics thereof are as follows: tensile strengthσ_(b)≧500 MPa, compressive strength σ_(bc)≧700 MPa, bending strengthσ_(bb)≧590 MPa, yield strength σ_(0.2)≧320 MPa, percentage elongationδ₅≧7%, Brinell Hardness HBS being 170˜230, and after the annealingtreatment, the metallographic structure of the base body becomingferrite+pearlite.

The technical means of the present invention are as follows:

A technology for preparing a nodular cast iron foundation pile pipe, thetechnology comprises following steps:

(1) preparation before pipe casting: including molten iron preparation,spheroidization and coating spraying on an inner wall of a pipe mold,

wherein the molten iron preparation includes heating the molten ironwith medium frequency furnace to a temperature of 1460° C.-1500° C., andmass fractions of main chemical compositions in the molten iron are:

C: 2.9-3.2%, Si: 1.4-1.6%, Mn≦0.5%, Ti≦0.04%, P≦0.06%, S≦0.020%;

the spheroidization includes using any of pour-over method, wire feedingspheroidizing method or pure magnesium spheroidizing method to spherizethe molten iron, mass fractions of main chemical compositions in thespheroidized molten iron are:

C: 3.0-3.3%, Si: 1.9-2.4%, Mn≦0.5%, P≦0.06%, S≦0.02%, Mg: 0.03-0.06%,Ti≦0.04%; and the spheroidized molten iron is conveyed to a castingprocess after slag removal;

the pipe mold is the die used for pipe casting, when casting the firstand second pipes, temperature of the pipe mold needs to be preheated to180° C.-260° C.; in case of continuous production, it is unnecessary topreheat the pipe mold every time before casting, since there is residualheat thereon.

In the coating spraying step, driven by a pipe mold rotating mechanism,the pipe mold with a residual heat of 180° C.-260° C. is caused torotate at low speed, the coating spraying trolley enters inside of thepipe mold along an axis of the pipe mold, and a spraying system startsto spray qualified mixture coating, after the thickness of the coatingand the surface of the coating is inspected and qualified, a sand coreis mounted at a socket part of the pipe mold for casting;

main components of the coating include diatomite, bentonite and water,and the coating is used after being uniformly stirred.

The thickness of the coating is 0.5 mm-1.0 mm.

(2) pipe casting process: including centrifugal casting and pipedrawing,

in the centrifugal casting, the spheroidized molten iron is poured intoa fan-shaped casting ladle, then slags are removed and the temperatureis measured, after the temperature reaches up to 1330° C.-1350° C., thecasting process is to be started; when a rotating speed of the pipe moldreaches to a predetermined value, the casting is started, aninstantaneous inoculation with respect to the molten iron is carriedout, and a secondary inoculant is instantaneously added into the molteniron while casting; the casting trolley draws back at a predeterminedspeed, after the casting is finished, the pipe mold is caused tocontinuously rotate for about 3 to 5 minutes and then water cooling isstarted, when the temperature of the pipe is lower than 600° C., thepipe drawing is started;

the inoculant is FeSiBas, the granularity thereof is 0.1 mm-0.7 mm, theaddition amount is 0.1%-0.25% (mass fraction).

The components of the inoculant are as follows.

Element Ba Si Ca Al Mn Cr P S Fe Content/ 5 67 2 <2 <0.4 <0.4 <0.04<0.02 Remainder %/Mass fraction

The pipe drawing includes drawing the pipe out of the rotating pipe moldby pipe drawing pliers after the casting is finished, when the pipe isdrawn out, two axial supporting rollers at a lower portion of acentrifugal pipe casting machine lift up respectively, and when the pipeis completely drawn out, the pipe drawing pliers disengage from thepipe. The supporting rollers are lowered and the pipe is placed on afixed rotating roller for continuous rotating and cooling, so as toprevent elliptical deformation, and then the pipe is conveyed to anannealing furnace with a rotary sling to carry out an annealing process;

(3) annealing process: carrying out annealing treatment to the pipe at atemperature of 720° C.-750° C. for 30 minutes, and the metallographicstructure of the base body after annealing becoming ferrite+pearlite.

(4) finishing process: after annealing, carrying out shot blastingtreatment to the coating and slag on a surface of the pipe, and carryingout finishing, hydrostatic test and preservative treatment, wherein thefinishing includes cutting pipe, straightening round and grinding, andthe pressure of the hydrostatic test is 2.5 MPa, the pressure holdingtime is 10 s.

The present invention further relates to a nodular cast iron foundationpile pipe prepared by the above preparation technology, wherein thefoundation pile pipe includes a pipe body and a flange disposed at anend portion of the pipe body.

Preferably, the diameter of the pipe body is 600-2000 mm and the lengththereof is 600-13000 mm, the diameter of the flange is 1000-2400 mm, andthe thickness thereof is 25-50 mm.

Preferably, the flange and the pipe body are integrally cast or welded.In case of welding the flange, a cast iron electrode is to be used, andthe welding portion is welded after being preheated.

The usage of pile pipe in the present invention is the same as that inthe prior art, that is, the pipe body of the pile pipe is struckunderground with the flange exposed on the ground, so as to function asthe foundation, and the pole is connected with the flange by bolts toform a whole.

Compared with the prior art, the present invention uses nodular castiron as the material of the pile pipe. In the nodular cast iron,spheroidal graphites are obtained by spheroidization and inoculation,thereby the mechanical properties of the cast iron being effectivelyimproved, especially the plasticity and toughness being improved, andthus a strength higher than that of carbon steel being obtained. Thecomprehensive property of the nodular cast iron is close to steel,therefore, it is used to cast components that bear complicated forcesand require high strength, toughness and abrasion resistance.

In the present invention, the nodular cast iron is used as the materialof the foundation pile pipe instead of Q345 steel used in the prior art,further, the flange and the foundation pile pipe are integrally cast orwelded, thereby the overall strength being enhanced. The presentinvention is featured with advantages such as corrosion resistance, longservice life, low manufacturing cost, low labor intensity, shortconstruction period and being suitable for mechanized construction andscale production by adopting centrifugal casting process.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is to be described in detail in combination withthe drawings and embodiments.

FIG. 1 is a structural schematic diagram of the foundation pile pipewelded with the flange of the present invention.

FIG. 2 is a structural schematic diagram of the integrally formedfoundation pile pipe and the flange of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A nodular cast iron foundation pile pipe and a technology for preparingsame, the technology comprises following steps:

(1) preparation before pipe casting: including molten iron preparation,spheroidization and coating spraying on an inner wall of a pipe mold,

wherein the molten iron preparation includes heating the molten ironwith medium frequency furnace to a temperature of 1460° C.-1500° C., andmass fractions of main chemical compositions in the molten iron are:

C: 2.9-3.2%, Si: 1.4-1.6%, Mn≦0.5%, Ti≦0.04%, P≦0.06%, S≦0.020%; thespheroidization includes using any of pour-over method, wire feedingspheroidizing method or pure magnesium spheroidizing method to spherizethe molten iron, mass fractions of main chemical compositions in thespheroidized molten iron are:

C: 3.0-3.3%, Si: 1.9-2.4%, Mn≦0.5%, P≦0.06%, S≦0.02%, Mg: 0.03-0.06%,Ti≦0.04%; and the spheroidized molten iron is set aside for later useafter slag removal;

the pipe mold is a die used for pipe casting, when casting the first andsecond pipes, temperature of the pipe mold needs to be preheated to 180°C.-260° C.; in case of continuous production, it is unnecessary topreheat the pipe mold every time before casting, since there is residualheat thereon.

In the coating spraying step, driven by a pipe mold rotating mechanism,the pipe mold with a residual heat of 180° C.-260° C. is caused torotate at low speed, the coating spraying trolley enters inside of thepipe mold along an axis of the pipe mold, and a spraying system startsto spray qualified mixture coating, after the thickness of the coatingand the surface of the coating is inspected and qualified, a sand coreis mounted at a socket part of the pipe mold for casting;

main components of the coating include diatomite, bentonite and water,and the coating is used after being uniformly stirred.

The thickness of the coating is 0.5 mm-1.0 mm.

(2) pipe casting process: including centrifugal casting and pipedrawing,

in the centrifugal casting, the spheroidized molten iron is poured intoa fan-shaped molten iron ladle, then slags are removed and thetemperature is measured, after the temperature reaches up to 1330°C.-1350° C., the casting process is to be started; when a rotating speedof the pipe mold reaches to a predetermined value, the casting isstarted, an instantaneous inoculation with respect to the molten iron iscarried out, and a secondary inoculant is instantaneously added into themolten iron while casting; the casting trolley draws back at apredetermined speed, after the casting is finished, the pipe mold iscaused to continuously rotate for about 3 to 5 minutes and then watercooling is started, when the temperature of the pipe is lower than 600°C., the pipe drawing is started;

the inoculant is FeSiBas, the granularity thereof is 0.1 mm-0.7 mm, theaddition amount is 0.1%-0.25% (mass fraction).

The components of the inoculant are as follows:

Element Ba Si Ca Al Mn Cr P S Fe Content/ 5 67 2 <2 <0.4 <0.4 <0.04<0.02 Remainder %/Mass fraction

The pipe drawing includes drawing the pipe out of the rotating pipe moldby pipe drawing pliers after the casting is finished, when the pipe isdrawn out, two axial supporting rollers at a lower portion lift uprespectively, and when the pipe is completely drawn out, the pipedrawing pliers disengage from the pipe. The supporting rollers arelowered and the pipe is placed on a fixed rotating roller for continuousrotating and cooling, so as to prevent elliptical deformation, and thenthe pipe is conveyed to an annealing furnace with a rotary sling tocarry out an annealing process;

(3) annealing process: carrying out annealing treatment to the pipe at atemperature of 720° C-750° C. for 30 minutes, and the metallographicstructure of the base body after annealing becoming ferrite+pearlite.

(4) finishing process: after annealing, carrying out shot blastingtreatment to the coating and slag on a surface of the pipe, and carryingout finishing, hydrostatic test and preservative treatment, wherein thefinishing includes cutting pipe, straightening round and grinding, andthe pressure of the hydrostatic test is 2.5 MPa, the pressure holdingtime is 10 s. The foundation pile pipe prepared by the above-mentionednodular cast iron foundation pile pipe preparation technology includes apipe body 1 and a flange 2 disposed at one end portion of the pipe body1, and the flange 2 and the foundation pile pipe 1 are integrally cast(as shown in FIG. 2) or welded (as shown in FIG. 1). The diameter of thepipe body 1 is 600-2000 mm and the length thereof is 600-13000 mm, thediameter of the flange 2 is 1000-2400 mm, and the thickness thereof is15-50 mm.

Two examples of the foundation pile pipes prepared by theabove-mentioned technology are as follows. A common size of thefoundation pile pipe is not limited to the following two examples. Andother sizes are determined according to actual requirements, which arenot to be listed here.

(1) The diameter of the pipe body 1 is 800 mm, and the length thereof is8000 mm; the diameter of the flange 2 is 1200 mm, and the thicknessthereof is 32 mm.

(2) The diameter of the pipe body 1 is 1100 mm, and the length thereofis 8000 mm; the diameter of the flange 2 is 1580 mm, and the thicknessthereof is 30 mm.

The above descriptions are only preferred embodiments of the presentinvention, and they are not intended to limit the scope of the presentinvention. Any equivalent substitution or modification made in thedisclosed technical scope of the present invention by a person skilledin the art, based on the technical proposal and the inventive concept ofthe present invention should be encompassed in the scope of the presentinvention.

1. A method for preparing a nodular cast iron foundation pile pipe, themethod comprises following steps: (1) preparation before pipe casting:including molten iron preparation, spheroidization and coating sprayingon an inner wall of a pipe mold, wherein the molten iron preparationincludes heating the molten iron with medium frequency furnace to atemperature of 1460° C.-1500° C., and mass fractions of main chemicalcompositions in the molten iron are: C: 2.9-3.2%, Si: 1.4-1.6%, Mn≦0.5%,Ti≦0.04%, P≦0.06%, S≦0.020%; the spheroidization includes using any ofpour-over method, wire feeding spheroidizing method or pure magnesiumspheroidizing method to spherize the molten iron, mass fractions of mainchemical compositions in the spheroidized molten iron are: C: 3.0-3.3%,Si: 1.9-2.4%, Mn≦0.5%, P≦0.06%, S≦0.02%, Mg: 0.03-0.06%, Ti≦0.04%; andthe spheroidized molten iron is set aside for later use after slagremoval; the coating spraying step includes spraying prepared coating onthe inner wall of the pipe mold, and mounting a sand core at a socketpart of the pipe mold for casting; (2) pipe casting process: includingcentrifugal casting and pipe drawing, wherein the centrifugal castingincludes adding a primary inoculant into the molten iron after the slagremoval and temperature measurement, pouring the molten iron into afan-shaped casting ladle, adding a secondary inoculant instantaneouslyinto the molten iron at the time of casting, and carrying out watercooling treatment after the casting is finished; the pipe drawingincludes drawing the pipe out of the pipe mold by pipe drawing pliersafter the casting is finished, the pipe continuously rotates during andafter the drawing process, and the pipe is conveyed to an annealingfurnace with a rotary sling; (3) annealing process: carrying outannealing treatment to the pipe at a temperature of 720° C.-750° C. for30 minutes; (4) finishing process: after annealing, carrying out shotblasting treatment to the coating and slag on a surface of the pipe, andcarrying out finishing, hydrostatic test and preservative treatment. 2.The nodular cast iron foundation pile pipe prepared by the methodaccording to claim 1, wherein the foundation pile pipe includes a pipebody and a flange disposed at an end portion of the pipe body.
 3. Thenodular cast iron foundation pile pipe according to claim 2, wherein adiameter of the pipe body is 600-2000 mm and a length thereof is600-13000 mm, a diameter of the flange is 1000-2400 mm, and a thicknessthereof is 15-50 mm.
 4. The nodular cast iron foundation pile pipeaccording to claim 2, wherein the flange and the pipe body areintegrally cast or welded.